1. Field of the Invention
The present invention relates to antennae for two-way communication, such as wireless telephones, and more particularly to planar antennae for such application.
2. Description of the Related Art
Wireless telephones, such as cellular and PCS telephones, commonly are used for mobile communication with passengers in vehicles. Such telephones usually have a hand-held unit which includes a microphone, a small speaker and a keypad for placing calls and controlling the operation of the telephone. The hand-held unit is coupled by a cable to an electronics module that contains a radio frequency transceiver. The transceiver in turn is coupled to an antenna on the exterior of the vehicle to send and receive the radio frequency signals. Cellular telephones transmit in the 824 to 845 MHz frequency band and receive signals in the 870 to 896 MHz frequency band. PCS telephones operate in the 1885 to 1990 MHz frequency band. Thus, an antenna that is tuned to operate with one type of these telephones would not be optimum for use with the other type.
A typical cellular telephone antenna for a motor vehicle is attached to the exterior surface of a window and comprises a short section of rigid wire extending vertically from the vehicle body. A coupling box is mounted on the interior surface of the window opposite to the antenna and is connected by a coaxial cable to the transceiver. The coupling box and the antenna are electrically coupled so that signals from the transmitter section of the transceiver are applied to the exterior wire from which the signals radiate. The coupling also allows radio frequency signals to be received by the exterior element and applied to the receiver section of the transceiver.
Even though such cellular telephone antennae are relatively short, protruding approximately one foot from the surface of the vehicle, they are subject to accidental breakage, such as in automatic car washes, and acts of vandalism. Although cellular telephone antennae are considered by some people to be a status symbol, others may consider them to be unsightly and a detraction from the aesthetic appearance of the vehicle.
U.S. Pat. No. 5,041,838 discloses a low profile, flat disk-shaped antenna for bidirectional communication, such as cellular telephones. This antenna is attached to a horizontal exterior surface of the motor vehicle, such as the roof. A coaxial cable extends through a hole in that surface, coupling the external antenna to the transceiver inside the motor vehicle. This antenna is tuned to a single frequency band.
U.S. Pat. No. 6,087,990 discloses a low profile, flat disk-shaped antenna assembly that combines two antennae into a single package. One antenna is tuned for bidirectional communication equipment, such as cellular telephones, while the other antenna in designed for another type of radio frequency equipment, such as a global positioning system receiver. Separate coaxial cables for each type of equipment connect to this dual antenna assembly.